1. Field of the Invention
The object of the invention contained herein is a process for the laser and/or plasma cutting of strips, particularly metal coils, and relative continuous cutting lines.
The invention has particular, but not necessarily exclusive, application in the mechanical engineering industry.
2. Description of Related Art
Laser or plasma cutting lines for plate are widely used, and the plates may be predisposed in the form of single sheets or continuous coils. The said type of plant is widely used in the industrial sector, for the production of large batches of components or for certain details which require extreme precision, and for pieces with either small or large dimensions.
In the cutting units of these machines, there is basically a fixed or mobile focusing head which is held at a short distance from the sheet by means of an accurate centering system (auto-focus), and which emits a perpendicular laser beam which penetrates the thickness of the material, and then carries out the cutting of the material.
The said apparatus, in the zone immediately below the focusing head, has to be equipped with special equipment which, on the one hand, by means of its particular conformation, helps to support the plate, while on the other hand helps to evacuate the toxic fumes and liquefied particles that are given off.
A typical example is made up of a cutting bed, which is sufficiently large to contain at least the maximum foreseen dimension of the plate to be cut, made up of a mesh or comb-type structure. One of the characteristics of the said cutting bed is given by the fact that, on the side that supports the plate, there is a series of protruding bodies with rounded tips, similar to nails. These nails keep the plate at a certain distance from the mesh structure, in order to help the cutting cycle. The mesh is also used to sift the swarf that results from the process, which falls through the mesh and is collected in a bin below the bed.
The bin works in conjunction with the above cutting bed, and has mechanical systems to evacuate the waste materials and motor-driven pumps to draw off all the liquefied particles and toxic fumes that are produced by the cutting head when it is in operation.
Regarding the focusing head of the cutting unit, there are currently two types available.
The first type has a static focusing head. In this case, the sheet is moved below the focusing head, and is held in place around its edges by a special clamping system, which grips the edges of the sheet. There is a logic unit which is programmed in order to communicate between the focusing head and the clamping system, in order to carry out a coordinated movement of the clamping system which thus moves the sheet in one direction or another.
The second type has a movable focusing head. In this case, the metal strip or sheet passes in the area below the head, moved step by step by means of a special transport mechanism. Going further into detail, since the cutting unit moves along two axes (x, y), the sheet is moved into position longitudinally and then held in a given position so that the cutting unit can carry out the cutting operation according to the program. Once the cutting cycle has been completed, the sheet is moved forward to leave the finished product, while the waste material is collected by the equipment positioned below the table. There is also a logic unit in the second case, which communicates between the pre-imposed movements of the cutting unit and the forward movement system for the strip or sheet. The movement phase is only carried out when the message is received from the logic unit, that is when the cutting cycle for each single piece has been completed.
With the solutions described above, even though they are both technically valid, there are various drawbacks.
Firstly, with both systems, once the piece has been cut and is still held in place by a micro-joint, it may fall into the area below the bed because of the movement and vibrations of the bed, especially of the protruding nails. The frequency of this event means that a number of cut pieces are accumulated or even lost in the equipment, below the cutting bed which is used for collecting and evacuating the cutting swarf, and which also interfere with the toxic fumes evacuation system. The material causes problems with both the waste recovery and fume evacuation systems, which results in a reduction of the efficiency of the systems and an increase in the amount of maintenance required.
Furthermore, from a technological point of view, the said equipment is rather complex and has a high manufacturing cost, and it is weighs quite heavily on the overall cost of the plant.
The plant also occupies a large amount of space. The cutting bed has to be sized according to the dimensions of strip or sheet which is to be processed, with a surface that is, therefore, at least large enough to hold each sheet. Regarding the work carried out on strips, the said apparatus, apart from the width of the bed, has to also take into consideration a cutting bed length which is sufficient for the longitudinal cutting cycle to be carried out. As a result, in order to carry out cuts on large objects, the area required for a correct installation of the plant has to be proportionally large.
As a consequence of the limits imposed by the existing equipment, the longitudinal cuts that can be carried out on the strips will depend on the size of the equipment. Therefore, with the current equipment available, it is not possible to cut pieces or details with an undefined length, or equal to the total length of the coiled strip.
The aim of this invention is also to overcome the aforementioned drawbacks.
This and other aims are achieved through the use of this invention according to the characteristics in the attached claims, solving the problems described by means of a laser or plasma cutting process for strips, especially metal coils, and relative continuous cutting lines in which a coil held on a reel is unwound upstream of the cutting line. In the said system, the strip is initially straightened and then moved downstream by a transport system towards a support bed. There is a focusing head positioned above the support bed, which is part of the laser or plasma cutting unit. The said focusing head, during the cutting cycle, is mobile along an axis, which is transversal with respect to the longitudinal movement of the strip. The said strip is moved downstream along an evacuation bed on which the both waste pieces and the finished pieces lay flat, and which are later separated.
In this way, through the creative contribution of the system, which leads to an immediate technical progress, various advantages are achieved.
The first advantage is given by the possibility of cutting pieces or details of an undefined length, or at least the overall length of the strip, which is not possible with any other type of plant.
The second advantage is given by the fact that the complex equipment and systems that are usually positioned below the cutting bed are eliminated, which reduces the transversal area required and is sized according to the fume and liquefied particles evacuation system, which in this case coincides with the travel axis of the focusing head.
By eliminating the equipment which includes the mechanical recovery of waste material from below the focusing head, maintenance operations are eliminated and there is no longer the risk of finished pieces, especially small ones, falling in the area below along with the waste material and being lost.
A further benefit regards the fact that the size and consumption figures for the plant are reduced, leading to an increased flexibility, due to the fact that small batches may also be produced, and an increase in productivity thanks to the availability of all the pre-imposed cutting parameters. Furthermore, the cutting path is optimised, there is good modulation of the power and, above all, the material is always on-line with no, or very little, time lost for changing the type of cycle to be carried out.
A further advantage is that the equipment is very reliable, the cost for buying and running the equipment is quite low, and the maintenance operations are reduced to a minimum.
These and other advantages will be explained in the following detailed description and attached schematic drawings of a preferred application of the system, the details of which are to be considered simply examples and not limitations of the system.